Introduction to Dfs

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					Introduction to Dfs
Limits of Dfs
•   260 characters per file path
•   32 alternatives per volume
•   1 Dfs root per server
•   Unlimited Dfs roots per domain
•   Volumes limited by system resources
Overview of Dfs Roots
• The Dfs Service is auto-installed with the installation of Microsoft
   Windows 2000 Server.
• Two types of Dfs roots can be configured on Windows 2000
   Server computers: stand-alone and domain.
Stand-Alone Dfs Roots
• Stand-alone Dfs information is stored in the local registry.
• A stand-alone Dfs root permits a single level of Dfs links.
• When the Distributed File System snap-in is used to connect to
    existing stand-alone Dfs roots, all servers known to the browse
    list are retrieved because there is no unique NetBIOS name
    registered by Dfs-enabled servers.
•   Stand-alone Dfs roots can be located on all supported file
    systems, although locating resources on NTFS-formatted
    partitions is recommended.
• Stand-alone Dfs roots offer no replication or backup; the Dfs
    root represents a single point of failure.
Domain Dfs Roots
• Multiple servers hand out referrals for the Dfs namespace.
• A fault-tolerant Dfs root is stored in Active Directory services and
   is replicated to every participating Dfs root server. Changes to a
   Dfs tree are automatically synchronized with Active Directory
• Fault-tolerant roots must be located on NTFS version 5.0–
   formatted partitions.
• The list of domains and servers is populated by querying the
   global catalog for all fault-tolerant Dfs roots.
• Dfs replication topology uses the existing Active Directory
   replication topology.
Configuring a Stand-Alone
Dfs Root
• Stand-alone Dfs stores the Dfs topology on a single computer
    and does not provide fault tolerance.
• A stand-alone Dfs root is physically located on the server that
    users initially connect to.
•   To create a stand-alone Dfs root, use the Distributed File System
    snap-in to start the New Dfs Root wizard.
Creating a Stand-Alone
Dfs Root
Configuring a Domain
Dfs Root
• Domain Dfs writes the Dfs topology to the Active Directory store,
   which allows links to point to multiple identical shared folders for
   fault tolerance.
• Domain Dfs supports DNS, multiple levels of child volumes, and
   file replication.
• To create a domain Dfs root, use the Distributed File System
   snap-in to start the New Dfs Root wizard.
Configuring New Dfs Links
• Users can browse folders under a Dfs root without knowing
   where the referenced resources are physically located.
• After you create the Dfs root, you can create Dfs links.
• To create a Dfs link, use the Distributed File System snap-in to
   open the Create A New Dfs Link dialog box.
Creating a Dfs Link
Dfs Links
FRS Replication
• FRS is installed automatically on all Windows 2000 Server
• FRS is configured to start automatically on all domain controllers
    and manually on all stand-alone and member servers.
•   The Active Directory store uses FRS to synchronize the directory
    among all the domain controllers.
•   Active Directory services automatically generates a ring topology
    for replication among domain controllers in the same domain.
•   The ring structure ensures that there are at least two replication
    paths from one domain controller to another.
Site and Domain Structures
• A site is made up of one or more IP subnets that identify a
    group of well-connected computers.
• Domain structure and site structure are maintained separately in
    Active Directory services.
•   A single domain can include multiple sites, and a single site can
    include multiple domains.
Single Domain with
Single Site
Single Domain with Multiple
Multiple Sites with Multiple
Intra-Site Replication
• Intra-site replication occurs between domain controllers
   within a site.
• Replicated data is not compressed.
• The default replication interval is five minutes.
• Replication is trigger-based (notification and pull).
Inter-Site Replication
• Inter-site replication occurs between domain controllers in
    different sites.
•   You can specify the time when inter-site replication should
    occur. The default replication interval is three hours.
• You can specify the network transport for use in inter-site
• Inter-site replication is compressed, regardless of the transport
•   Inter-site replication compression reduces the data on the
    network by 88 to 90 percent.
• Inter-site replication is not configured automatically; it must be
    configured by an administrator.
Knowledge Consistency
Checker (KCC)
• The KCC generates a ring topology for replication among domain
    controllers in the same domain.
• The ring structure guarantees that there are at least two
    replication paths from one domain controller to another.
•   The KCC analyzes the replication topology within a site to ensure
    that the replication topology is efficient.
Unique Sequence Numbers
• When a directory object is updated at a domain controller, a
    USN is assigned.
• When the domain controller writes the change into the directory,
    it also writes the USN.
•   Each domain controller maintains a table of the USNs that it
    receives from every other domain controller in the domain.
•   USNs eliminate the need for precise time stamps for changes.
•   USNs simplify recovery after a failure.
Replicating SYSVOL
• Changes to the %systemroot%\SYSVOL folder on any domain
   controller are automatically replicated to other domain
   controllers within the site.
• The replication topology and process are separate but identical
   to Active Directory replication.
• Windows 2000 Server sets up a default folder structure for
Replicating Dfs
Fault-Tolerant Roots
• Dfs and file replication support a number of features.
• Each Dfs root or link can reference a replicated set of share
•   Dfs replication is disabled by default; use the Distributed File
    System snap-in to enable replication.
Configuring FRS for
Inter-Site Replication
• Use the Active Directory Sites And Services snap-in to configure
   inter-site replication.
• To configure the FRS settings, you must create a new site link
   for the inter-site transport protocol listed in the console tree.